Influenza viruses mutate rapidly. Therefore, the formulation of seasonal flu vaccines must be updated annually. Vaccine effectiveness is influenced by the similarity between the viruses the vaccine is designed to protect against, and viruses actually spreading during the epidemic. Effectiveness must be assessed annually, preferably already as the season unfolds, so that the World Health Organization can use the information at the end of February when drafting its recommendations on the composition of influenza virus vaccines for the following season.
For a long time already, attempts have been made to develop a ”universal” influenza vaccine, which would consist of permanent components of the influenza virus, such as the virus surface proteins haemagglutinin and neuraminidase. The task has proved more difficult than anticipated. In the “galactic” strategy, different vaccines are manufactured for persons of different ages and different risk groups instead of a universal vaccine. It leads to a diversification of the range of seasonal influenza vaccines, while also presenting challenges to the assessment of product-specific effectiveness.
Finland has already introduced an intranasal live attenuated influenza vaccine for children, in addition to the split whole-virus vaccine and a vaccine containing virus surface structures. Influenza vaccines also differ in terms of valency, in other words, how many different viruses are included in the vaccine: in the last season, there was discussion on whether the quadrivalent flu vaccine had provided a higher degree of protection than the trivalent vaccine.
Member states of the European Union are in unequal positions: all influenza vaccines available on the market are not registered centrally in the EU but nationally. Thus, for example, the elderly in Italy have been protected with a vaccine containing an adjuvant. In the United States, a high-dose vaccine has been used to protect the elderly, containing four times the virus antigen of standard vaccines. Such vaccines may, according to current knowledge, provide slightly better protection for the elderly.
The newest addition soon arriving to the European market is a cell-based vaccine. It is hoped that it will resolve a problem related to the previous production methods, which has reduced the effectiveness of the A(H3N2) virus component especially amongst older people.
The protective effectiveness of seasonal influenza vaccines is investigated annually in many countries, including Finland. The I-MOVE and I-MOVE+ projects funded by the European Centre for Disease Prevention (ECDC) and the European Commission have laid the foundation for European cooperation in the assessment of influenza vaccines’ effectiveness in the past eleven years. For the time being, the published studies have assessed influenza vaccines as a whole, and product-specific information has not been presented.
The European Medicines Agency (EMA), which supervises the marketing authorisation of vaccines, made the requirements of influenza vaccines more stringent last year.
Now all manufacturers of influenza vaccines are required to present product-specific evidence on influenza vaccines’ effectiveness.
EMA also took into account in its guidelines the European public health institutes’ long experience in vaccine research, and recommended cooperation with the public sector to the vaccine manufacturers.
It is a demanding task to assess the effectiveness of all influenza vaccines on the European market, and it requires extensive research. It is also necessary to know how to interpret product-specific information. Multiple factors affect the effectiveness of vaccines. Individual surveys, possibly carried out in different populations during various influenza seasons and using different methods, carry a risk of leading to hasty conclusions on the superiority of different products. Nonetheless, product-specific information is required. The question remains how to organise the research in a transparent and non-discriminatory way.
The international DRIVE consortium develops methods for assessing the product-specific effectiveness of influenza vaccines. From the beginning, the National Institute for Health and Welfare has been at the heart of the consortium. Finland’s strategy in DRIVE is to promote the transparency of the cooperation and data re-use. Our country’s comprehensive national registers – in particular, the registers of vaccinations and infectious diseases, as well as care registers of hospitals and health centres – play a key role. They can answer questions such as how effective the intranasal vaccine is, does the quadrivalent vaccine offer better protection than the trivalent one, is the cell-based vaccine more effective than the egg-based one, and whether the differences in effectiveness are substantial enough to make it worthwhile to spend tax money on the additional benefit. Everyone will benefit from this information: in addition to the EMA and WHO, citizens and health professionals, as well as vaccine manufacturers.
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